Genetic variation and phylogenetic analyses of conserved Lanyu pigs and exotic pig breeds in Taiwan by microsatellite markers
|Keywords:||蘭嶼豬;微衛星標記多型性;哈溫平衡;近親配種;遺傳距離;Lanyu pig;microsatellite marker;polymorphisms;Hardy-Weinberg equilibrium;inbreeding;genetic distance||Issue Date:||2006||Abstract:||
為了釐清以上之問題。此次研究利用微衛星標記之多型性，探討蘭嶼豬族群內之遺傳多型性及與臺灣外來豬種之類緣關係，並期望作為日後族群管理之參考。自農委會畜試所種原庫、臺東種畜繁殖場、高雄種畜繁殖場與國立臺灣大學取得桃園豬、梅山豬、藍瑞斯、蘭嶼豬、杜洛克、與約克夏7個豬種共242頭之血液檢體。並抽取其Genomic DNA後，經螢光標定之引子對豬15對染色體上之19個微衛星標記以PCR方式進行增幅。再以毛細管電泳之方式測定增幅後之片段長度，並根據其多型性估算此7豬種間之遺傳距離。結果顯示蘭嶼豬與梅山豬、盤克夏與約克夏間有較近之遺傳距離。而以遺傳距離建構7豬種間之Neighbor-Joining tree（NJ tree）並經1000次再取樣分析，結果顯示7個豬種間形成兩個主要且穩定之分支（bootstrap value = 99.6），其一包含藍瑞斯、杜洛克、盤克夏與約克夏4個歐美豬種。另一則由桃園豬、梅山豬與蘭嶼豬3個亞洲豬種所構成，且蘭嶼豬於此分支中又另形成一獨立分支（bootstrap value = 73.6）。此外根據7豬種242個個體間之遺傳距離所建構之NJ tree顯示，保種蘭嶼豬44個個體構成一獨立之分支。且未混入其他豬種。綜合以上族群與個體間之NJ tree結果顯示蘭嶼豬與上述6個臺灣地區外來豬種基因交流之可能性低，而為一獨特之豬種。
The Lanyu pig is an indigenous pig breed from Lanyu Islet and is classified as a miniature pig breed. For the purpose of developing laboratory swine, Lanyu pigs were introduced into Taiwan by the Department of Animal Husbandry, National Taiwan University and Taitung Animal Propagation Station in 1975 and 1980, respectively. These pigs were reared in isolation as two herds and performed random mating until 2004. The genetic diversity within all the conserved Lanyu pigs remained unknown. Many exotic pigs breeds including Taoyuan, Meishan, Landrace, Duroc and Yorkshire breeds were introduced into Taiwan during 1877~1994. It is possible the genes of these exotic pigs introgress into Lanyu pigs after 1877.
The aims of the present study were to investigate the genetic variation within conserved Lanyu pigs and the genetic lineage among Lanyu and exotic pig breeds in Taiwan by polymorphisms of microsatellite markers. Genomic DNAs of 242 individuals from Lanyu, Taoyuan, Meishan, Landrace, Duroc, Yorkshire and Berkshire were extracted. Nineteen microsatellite markers were applied in this study that separately located on 15 porcine chromosomes, and were amplified using fluorescence dye labelled primers by PCR. The fragment length polymorphisms of each microsatellites were analyzed by capillary electrophoresis, based on polymorphisms of these microsatellites. The genetic distance were applied for studying the phylogenetic relationships among these pig breeds. The result showed that Lanyu pig had the shortest genetic distance with Meishan (0.2254), Berkshire (0.2351) and Yorkshire (0.2368) compared to the other exotic breeds. The neighbor-joining (NJ) tree was constructed by genetic distance from seven pig breeds with 1000 bootstarp resampling. It showed that the 7 breeds formed 2 major clades (bootstrap value = 99.6), one composed of all the exotic European breeds, and the Asian breeds were classified into another clade, including Lanyu Taoyuan and Meishan pig breeds, and in Asian clade, Lanyu formed a unique subclade (bootstrap value = 73.4). The Neighbor-Joining tree based on genetic distance among 242 individuals of 7 breeds in this study was constructed. All individuals of Lanyu pigs were clustered into a unique clade in NJ tree, suggesting that the conserved Lanyu pigs didn’t suffer gene introgression from exotic pig breeds.
Our data showed 15 of 19 microsatellite loci in Lanyu pigs genome deviating from Hardy-Weinberg equilibrium and FIS value of 19 microsatellite loci were all positive, indicated that inbreeding or Wahlund effect during rearing the conserved Lanyu pigs. For the purpose to prevent the inbreeding depression and maintain the genetic diversity of Lanyu pig, the population structure of Lanyu pig was constructed according to microsatellite polymorphisms. The Lanyu pigs was divided as 4 subpopulations, all individuals of NTU herd were formed an independent subpopulation with the probability higher than 80%. The Lanyu pigs in TAPS could be separated into another 3 subpopulations. This result indicated Lanyu pigs in NTU formed the different allele frequency of microsatellite loci from TAPS, the genetic distance between this two populations also supported this result.
In conclusion, the Lanyu pig is a unique breed without gene introgression from exotic pig breeds, but it had sustained loss of heterozygosity. In future, these results can be applied in population management of Lanyu pig to maintain the genetic diversity and as a guideline for producing inbreed laboratory Lanyu breed.
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